1. Field of the Invention
The present invention relates to a medical bag having excellent sanitariness, flexibility, transparency, and heat-resistance and suitable for use as a container for blood and medicinal liquids. More specifically, it relates to a medical bag composed of a sheet having a structure of three or four layers or more each comprising a polyethylene resin or the composition thereof, and is intended to provide a medical bag having excellent sanitariness, flexibility, transparency, and heat-resistance and suitable for use as a container for blood and medicinal liquids.
2. Description of the Related Art
Rigid containers made of, for example, glass, polyethylene, polypropylene or other material, and flexible bags made of poly (vinyl chloride) containing plasticizers are heretofore known as medical containers or bags. The rigid containers, however, have disadvantages in that air is introduced into the containers using a transfusion set provided with a vent needle or hole when the liquid contained therein is dropwise introduced into a human body through, for example, a vein, and therefore, the liquid contained therein might be contaminated and air can enter the vein to cause an air embolus therein. Thus, these rigid containers do not completely satisfy the requirements of sanitariness and safety. On the other hand, the flexible bags have advantages in that the introduction of air is not required and the bag itself is naturally compressed under atmospheric pressure with the dropwise introduction of the liquid contained therein, so that the safety is high and the transportation of the bag is easy. Flexible bags, however, have problems caused by, for example, plasticizers contained in polyvinyl chloride and the toxicity of residual monomers. The use of these flexible bags, especially those made of non-rigid poly(vinyl chloride), however, involves possible problems caused by migration of plasticizers into the liquid contained in the bags and the toxicity of the vinyl chloride monomer contained in the poly(vinyl chloride).
A medical bag, wherein a polymer, such as an ethylene-vinyl acetate copolymer or an elastomer, was used as an intermediate layer, has been proposed as a medical bag having excellent flexibility, transparency and sanitariness (see Japanese Unexamined Patent Publication (Kokai) No. 58-165866). The heat resistance of the polymer used in the intermediate layer is so poor that wrinkles occur in the bag during thermal sterilization treatment, which deteriorates the appearance of the medical bag.
In view of the above, some of the present inventors have conducted various studies on a medical bag having excellent sanitariness, flexibility, transparency, heat resistance and suitable for use as a container for blood and medicinal liquids and, as a result, have found that the above-mentioned property requirements can be satisfied when the medical bag is composed of a sheet having a three-layer structure each comprising a polyethylene resin, and previously proposed (see Japanese Unexamined Patent Publication (Kokai) Nos. 62-44256 and 62-64363).
In the medical bag according to the invention described in the above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 62-44256, the outer and inner surface layers each comprise a low-density polyethylene resin produced in the presence of a radical catalyst (the intermediate layer comprising a linear low-density polyethylene resin). Since, however, the outer surface layer of the proposed medical bag comprises a low-density polyethylene resin, the medical bag is not always satisfactory in heat resistance, so that the medical bag cannot be successfully subjected to a high-pressure steam treatment at a temperature of 120.degree. C. For example, since the sealing strength is unsatisfactory, the medical bag cannot be successfully treated with a high-pressure steam sterilization treatment at a temperature of 120.degree. C. for 20 minutes. The typical conditions of the high-pressure steam sterilization are, for example, 115.degree. C..times.30 minutes and 121.degree. C..times.20 minutes. Further, the medical bag is unsatisfactory also in the drop impact strength. Further, the flexibility and transparency lower, and some deformation occurs.
In order to solve these problems, some of the present inventors have proposed in Japanese Unexamined Patent Publication (Kokai) No. 4-266759 a method which enables the medical bag to withstand sterilization with a high-pressure steam at a high temperature of 121.degree. C. through an improvement in the composition constituting the inner and outer layers. This method can surely provide a medical bag which gives rise to no significant deformation, is less subject to a lowering in the sealing strength and drop impact strength and can maintain the flexibility and transparency even when exposed to a high-pressure steam at a temperature of 121.degree. C. in the sterilization, and enables molding to be stably conducted even in continuous production for a long period of time. Even the above-mentioned formulation caused a large amount of fine particles to sometimes elute into a liquid contained in the bag depending upon the type of contents after the sterilization with a high pressure steam at a temperature of 121.degree. C. for 20 minutes, so that a sanitary problem may occur.